Linear array ultrasound transducer with microbeamformer

ABSTRACT

An ultrasonic diagnostic imaging system has a two dimensional array arranged in multiple patches of multiple transducer elements. Each patch of transducer elements is coupled to a group of microbeamformer delay lines having outputs coupled to a channel of a system beamformer, which beamforms the partially summed beams of each patch into a final beamformed signal. The outputs from multiple patches which are not simultaneously used in the active receive aperture are coupled to a common beamformer channel, enabling the number of patches of the array to exceed the number of channels of the system beamformer without the use of multiplexers.

This invention relates to medical diagnostic ultrasound systems and, inparticular, to linear array ultrasound transducers withmicrobeamformers.

Ultrasonic array transducers use beamformers to receive andappropriately delay the ultrasonic echo signals received from elementsof the transducer array. The delays are chosen in consideration of thedirection (steering) and focusing of the beams to be formed by thebeamformer. After the signal from each element has been properly delayedby a channel of the beamformer, the delayed signals are combined to forma beam of properly steered and focused coherent echo signals. The choiceof delays are known to be determinable from the geometry of the arrayelements and of the image field being interrogated by the beams. In atraditional ultrasound system the array transducer is located in a probewhich is placed against the body of the patient during imaging andcontains some electronic components such as tuning elements, switches,and amplification devices. The delaying and signal combining isperformed by the beamformer which is contained in the ultrasound systemmainframe, to which the probe is connected by a cable.

The foregoing system architecture for an array transducer and abeamformer suffices quite well for a one dimensional (1D) transducerarray, where the number of transducer elements and the number ofbeamformer channels are approximately the same. When the number oftransducer elements exceeds the number of beamformer channels,multiplexing is generally employed and only a subset of the total numberof elements of the transducer can be connected to the beamformer at anypoint in time. The number of elements in a 1D array can range from lessthan one hundred to several hundred and the typical beamformer has 128beamformer channels. This system architecture solution became untenablewith the advent of two dimensional (2D) array transducers for threedimensional (3D) imaging. That is because 2D array transducers steer andfocus beams in both azimuth and elevation over a volumetric region. Thenumber of transducer elements needed for this beam formation is usuallyin the thousands. The crux of the problem then becomes the cable thatconnects the probe to the system mainframe where the beamformer islocated. A cable of several thousand conductors of even the finestconductive filaments becomes thick and unwieldy, making manipulation ofthe probe cumbersome if not impossible.

A solution to this problem is to perform at least some of thebeamforming in the probe itself, as described in U.S. Pat. No. 5,229,933(Larson, III). In the ultrasound system shown in this patent, thebeamforming is partitioned between the probe and the system mainframe.Initial beamforming of groups of elements is done in the probe, wherepartially beamformed sums are produced. These partially beamformed sums,being fewer in number than the number of transducer elements, arecoupled to the system mainframe through a cable of reasonabledimensions, where the beamforming process is completed and the finalbeam produced. The partial beamforming in the probe is done by whatLarson, III refers to as an intragroup processor, or microbeamformer inthe form of microelectronics attached to the array transducer. See alsoU.S. Pat. No. 5,997,479 (Savord et al.); U.S. Pat. No. 6,013,032(Savord); U.S. Pat. No. 6,126,602 (Savord et al.); and U.S. Pat. No.6,375,617 (Fraser). The thousands of connections between the 2Dtransducer array and the microbeamformer is done at the tiny dimensionsof the microcircuitry and the array pitch, while the cable connectionsbetween the microbeamformer and the beamformer of the system mainframeare done by more conventional cable technologies. Various planar andcurved array formats can be used with microbeamformers such as thecurved arrays shown in U.S. patent applications 60/706,190 (Kunkel) and60/706,208 (Davidsen).

The microbeamformers shown in the above patents operate by formingpartially delayed sum signals from contiguous element groups referred toas “patches.” The signals received by all of the elements of a patch areappropriately individually delayed, then combined into the partial sumsignal. A ramification of the patch approach is that aperture design isbased upon the number, size and shape of the array patches. This worksvery well for a 2D phased array transducer, where the full arrayaperture is used during echo reception. But for linear array operation,where the active array aperture is translated across the 2D array, thepatch size and dimensions can place constraints on aperture translation.The stepping of the active aperture is generally required to be done inpatch-sized increments, for example, as shown in the aforementioned U.S.Pat. No. 6,013,032 (Savord). Accordingly it is desirable for a 2D arrayto be operable for aperture translation in lesser increments withoutadding complexity to the microbeamformer. It would further be desirableto be able to operate the same microbeamformer for either linear arrayor phased array operation.

In accordance with the principles of the present invention, a twodimensional array and microbeamformer are operated for linear arrayscanning of a volumetric region. The active array aperture is steppedacross the array in increments smaller than the dimensions of an elementpatch, which can be as small as a single transducer element. The partialsum signals from more than one patch can be coupled over the sameconductor to the system mainframe beamformer by use of patch andaperture configurations which do not place conflicting signals on thesame conductor at the same time. Thus, the number of patches can exceedthe number of cable conductors and mainframe beamformer channels, evenfor unmirrored (asymmetrical) apertures. An embodiment of the presentinvention can allow arrays with very large numbers of elements to beused with a conventionally sized mainframe beamformer. An embodiment ofthe present invention may be configured for use in either linear orphased array mode of operation.

In the drawings:

FIG. 1 illustrates in block diagram form a 2D curved array transducerand microbeamformer probe of the present invention.

FIG. 2 is a block diagram illustrating the concept of a partial beamsummicrobeamformer.

FIG. 3 is a block diagram of one example of a 2D array transducer andmicrobeamformer constructed in accordance with the principles of thepresent invention.

FIGS. 4, 5, and 6 illustrate detailed examples of a microbeamformerdelay line.

FIG. 7 is a second example of a 2D array transducer and microbeamformerconstructed in accordance with the principles of the present invention.

FIG. 8 is a third example of a 2D array transducer and microbeamformerconstructed in accordance with the principles of the present invention.

FIGS. 9, 12, 13, and 14 illustrate a further example of the presentinvention in which the boundaries of a patch are made arbitrary.

FIGS. 10 and 11 illustrate switch configurations suitable for use in theexamples of FIGS. 9, 12, 13, and 14.

Referring first to FIG. 1, an ultrasound system constructed inaccordance with the principles of the present invention is shown inblock diagram form. A probe 10 has a two dimensional array transducer 12which is curved in the elevation dimension as shown in theaforementioned Davidsen patent application. The elements of the arrayare coupled to a microbeamformer 14 located in the probe behind thetransducer array. The microbeamformer applies timed transmit pulses toelements of the array to transmit beams in the desired directions and tothe desired focal points in the three dimensional image field in frontof the array. Echoes from the transmitted beams are received by thearray elements and coupled to channels of the microbeamformer 14 wherethey are individually delayed. The delayed signals from a contiguouspatch of transducer elements are combined to form a partial sum signalfor the patch. In the examples below combining is done by coupling thedelayed signals from the elements of the patch to a common bus,obviating the need for summing circuits or other complex circuitry. Thebus of each patch is coupled to a conductor of a cable 16, whichconducts the partial sum patch signals to the system mainframe. In thesystem mainframe the partial sum signals are digitized and coupled tochannels of a system beamformer 22, which appropriately delays eachpartial sum signal. The delayed partial sum signals are then combined toform a coherent steered and focused receive beam. The beam signals fromthe 3D image field are processed by a signal and image processor 24 toproduce 2D or 3D images for display on an image display 30. Control ofultrasound system parameters such as probe selection, beam steering andfocusing, and signal and image processing is done under control of acontroller 26 which is coupled to various modules of the system. In thecase of the probe 10 some of this control information is provided fromthe system mainframe over data lines of the cable 16. The user controlsthese operating parameters by means of a control panel 20.

FIG. 2 illustrates the concept of a partially summing microbeamformer.The drawing of FIG. 2 is sectioned into three areas by dashed lines 32and 34. Components of the probe 10 are shown to the left of line 32,components of the system mainframe are shown to the right of line 34,and the cable 16 is shown between the two lines. The two dimensionalarray 12 of the probe is divided into patches of contiguous transducerelements. Five of the patches of the array 12 are shown in the drawing,each including nine neighboring elements. The microbeamformer channelsfor patches 12 a, 12 c, and 12 e are shown in the drawing. The nineelements of patch 12 a are coupled to nine delay lines of themicrobeamformer indicated at DL1. Similarly the nine elements of patches12 c and 12 e are coupled to the delay lines indicated at DL2 and DL3.The delays imparted by these delay lines are a function of numerousvariables such as the size of the array, the element pitch, the spacingand dimensions of the patch, the range of beam steering, and others. Thedelay line groups DL1, DL2, and DL3 each delay the signals from theelements of their respective patch to a common time reference for thepatch. The nine delayed signals from each group of delay lines are thencombined by a respective summer Σ to form a partial sum signal of thearray from the patch of elements. Each partial sum signal is put on aseparate bus 15 a, 15 b, and 15 c, each of which is coupled to aconductor of the cable 16, which conducts the partial sum signals to thesystem mainframe. In the system mainframe each partial sum signal isapplied to a delay line 22 a, 22 b, 22 c of the system beamformer 22.These delay lines focus the partial sum signals into a common beam atthe output of the system beamformer summer 22 s. The fully formed beamis then forwarded to the signal and image processor for furtherprocessing and display. While the example of FIG. 2 is shown with9-element patches, it will be appreciated that a constructedmicrobeamformer system will generally have patches with larger numbersof elements such as 12, 20, 48, or 70 elements or more. The elements ofa patch can be adjacent to each other, be spaced apart, or evenintermingled in a checkerboard pattern, with “odd” numbered elementscombined in one patch and “even” numbered elements combined in another.The patches can be square, rectangular, diamond-shaped, hexagonal, orany other desired shape.

FIG. 3 shows another example of a two dimensional array transducer andmicrobeamformer of the present invention. This drawing shows three rowsR1, R2, and R3 of a two dimensional array transducer 12. In this examplea patch of elements consists of four elements: elements e1-e4 form onepatch, elements e5-e8 form another patch, elements e9-e12 form a furtherpatch, and so on. The elements of each patch are coupled to the delaylines of a group of microbeamformer delay lines. For example, elementse1-e4 are coupled to the four delay lines of delay line group DL1,elements e5-e8 are coupled to the delay lines of delay line group DL2,and so on. The delayed signals from a delay line group are combined onan output bus which connects the delay line outputs together. Forexample the four delay line outputs of group DL1 are all tied to bus b1,the four delay line outputs of group DL2 are connected to bus b2, and soon. Each bus is connected to an individual conductor of the cable 16.Bus b1 is connected to conductor 16 a of the cable, and bus b2 isconnected to cable conductor 16 b, and so on. Each cable conductor leadsto a channel of the system mainframe beamformer.

During transmit a group of elements of the array are activated totransmit the desired beam in the desired direction. The group chosen fortransmit will generally be small for a near field focused beam, and canbe as large as the entire array for a far field beam. The elementsactivated for the transmit beam, referred to as the transmit aperture,can occupy any shape or pattern of elements on the array. A zonefocusing scheme, which focuses at progressively deeper focal zones, canuse progressively larger transmit apertures for each deeper zone, forinstance. A transmit beam can be steered straight ahead (normal to thesurface of the array), or be steered at an angle to the array surface.In the probe shown in the Davidsen patent application, the beams aresteered straight ahead at the interior of the array, and at outwardcanted angles around the periphery of the array to create a wider fieldof view.

The transducer array and microbeamformer of FIG. 3 can be operated as alinear array or as a phased array. Linear array operation is done bytransmitting beams from apertures which are moved along the surface ofthe array and receiving the echoes from these beams at receive apertureswhich are also moved along the surface of the array. In the exampleshown in the drawing a receive aperture size is bracketed at the top ofthe drawing and in this example is seen to be three patches (twelveelements) wide. In this example the receive aperture is illustrated asbeing a single row (R1) high, but it could alternatively be multiplerows high. A first receive beam is received by elements e1-e12 in thisexample. Since this receive aperture includes the first three patches inrow R1 of the array, the delay lines DL1, DL2, and DL3 (not shown) ofthese first three groups in the microbeamformer are enabled for thisbeam. The delay lines are enabled in this example by enable lines Enconnected to each delay line as indicated at 42, 44, and 46. The fourdelayed signals from elements e1-e4 and delay line group DL1 areconnected to bus b1 where they are combined to form a partial sum signalfrom the first patch. Similarly, the four delayed signals from elementse5-e8 and delay line group DL 2 are combined on bus b2 and the fourdelayed signals from elements e9-e12 and delay line group DL3 arecombined on bus b3 (not shown). The busses are operated as summing nodesfor the formation of the partial sum signals in this example. The threebuses and cable conductors conduct these partially beamformed signals tothree channels of the main beamformer, where the beamformation of thebeam is completed.

The next beam is acquired by stepping the receive aperture to the rightin this example. The beam could be stepped by an entire patch by use of,for example, multiplexers in the cable connector or ultrasound systemmainframe, resulting in the next beam being acquired by a receiveaperture consisting of elements e5-e16. However this translation of anentire patch width would result in a coarse beam spacing across theimage field. In this example finely spaced beams are acquired bystepping the receive aperture by less than the dimension of a fullpatch, and preferably by a single element width. The next beam is thusacquired by elements e2-e13. Since the signal from element e1 does notcontribute to this beam, the enable line to the microbeamformer delayline for this element disables this delay line from contributing to thisnext beam. Only the delayed signals from elements e2-e4 are combined onbus b1. Since the signal from element e13 is contributing to this beam,the microbeamformer delay line for this element is enabled and thedelayed signal placed on the bus b4 (not shown) for that delay linegroup. The partial sum signals on four buses are coupled to the mainbeamformer for completion of the beamformation process: three combinedsignals on bus b1 from elements e2-e4, four combined signals on buses b2and b3, and the signal from element e13 on bus b4. Apodization weightingis employed in the main beamformer to account for the unequal signalweighting on the different buses.

The stepping of the receive aperture across the array continues in thismanner. The next beam uses elements e3-e14 for the receive aperture, thefollowing beam uses elements e4-e15, and the subsequent beam useselements e5-e16 for reception. As this stepping occurs it is seen thatthe delay lines of the first patch DL1 are progressively disabled whilethe delay lines of the fourth patch which are connected to elementse13-e16 are progressively enabled. The last of these beams is seen touse no elements from the first patch. With the next beam step to anaperture of elements e6-e17 it is seen that the first delay line ofdelay line group DL5 is enabled. The outputs of this fifth delay linegroup are in this example connected to bus b1, for it is seen that theaperture at no time uses elements from both the first and fifth patchesfor the same beam. Thus, as the delay lines of the first patch becomefully disabled, the delay lines of the fifth delay line group DL5 beginusing the same bus b1 previously used by delay line group DL1. These twogroups cannot use the same bus at the same time because their partialsum signals require different delays for beamformation in the mainbeamformer. If these partial sum signals were combined on a common bus,they could not be subjected to the necessary delay difference in theirprocessing. Thus, by considering the apertures used by the array,multiple patches can be connected to the same cable conductors to themain beamformer, which means that the number of patches can exceed thenumber of conductors in the cable. A greater number of array patches cantherefore be accommodated by a given cable and system beamformer. Withthe ability to increase the number of patches for a given array, thesize of the patches can be decreased, thereby reducing the delay lengthsneeded in the microbeamformer.

In this example it is seen that the delay line group DL9 for the patchat the right side of the array can also be connected to bus b1. Thedelay line group DL5 is progressively disabled as the delay line groupfor elements e29-e32 are progressively enabled. After delay line groupDL5 is fully disabled, the aperture progresses to the right as the delaylines of group DL6 are progressively disabled and the delay lines ofgroup DL9 are progressively enabled. Since both groups DL1 and DL5 aredisabled during this later stepping of the aperture, delay line groupDL9 can be connected to and is free to use bus b1 at this time.

The receive aperture will continue to step across the array in thismanner which, in this example, will acquire twenty-five different beamsat twenty-five different beam locations before the aperture reaches theright side of the array. This stepping process can then be repeatedacross the second row R2 of the array and then the third row R3. In thismanner a volumetric field in front of the array is scanned for 3Dimaging. Variations to the illustrated aperture will readily occur tothose skilled in the art. For instance, an aperture can be more than asingle row high. An aperture could begin with elements e1-e12 of thefirst row R1 and the first twelve elements of row R2. This twenty-fourelement aperture can be stepped across the array, then stepped up by onerow. The next translation would begin with the first twelve elements ofeach of rows R2 and R3 as the active aperture, which would then stepacross the array. Various aperture translation patterns can also beemployed. For instance, the active aperture can begin at the bottom ofthe array and step to the top, then across and back down the array, andso on in this manner. A translation sequence which steps the apertureacross and up in a roughly diagonal direction can also be employed.Aperture translation patterns can be chosen to minimize motion artifactsin regions of the image field, for instance.

The delay lines of a system of the present invention can be eitherdigital or analog delay lines, depending upon whether the signals aredigitized prior to the delay lines. A preferred analog delay line isshown in FIG. 4. This delay line is formed by coupling successivesignals from a transducer element to capacitors of a capacitor bank.Three capacitors 52, 54, 56 of such a capacitor bank are shown in FIG.4. The number of capacitors in the capacitor bank is chosen inconsideration of the maximum length of delay needed and the samplingrate used. A longer delay and/or finer resolution (e.g., to satisfy theNyquist criterion) requires a greater number of capacitors. The timedelay of the delay line is effected by writing a voltage sample from thetransducer element e_(n) onto a capacitor at an earlier time, thenreading the voltage sample from the capacitor at a later time, theincremental time between writing and reading providing the delay time.The capacitor bank can be arranged in a parallel configuration as shownin FIG. 4, or in a serial configuration in the manner of a CCD chargebucket brigade as discussed in U.S. Pat. No. 6,126,602 (Savord et al.)

In the configuration of FIG. 4 the echo signals from a transducerelement en are applied by way of a buffer amplifier 68 to the inputs ofa bank of input switches 64. The closure of each switch is controlled bya control signal from a write pointer 60. For instance, a first signalsample may be stored on capacitor 52 by momentary closure of its inputswitch, a second sample is stored on capacitor 54, a third sample isstored on capacitor 56 and so on. At a later time determined by thedesired delay time the samples are read from the capacitors in sequencedetermined by control signals from a read pointer 62 which control anoutput bank of switches 66. In the illustrated example an echo signalsample is being written to capacitor 52 while and echo signal sample isbeing read from capacitor 54. As an output switch is closed the signalsample on the capacitor is applied to the output bus bn which conductsthe signal to the cable conductor 16 n. While samples from the delayline of FIG. 4 are being applied to the output bus bn, samples fromother delay lines of the patch delay line group are simultaneously beingapplied to the same bus bn. The simultaneous application of the signalsthus results in a summation of the delayed samples from the elements ofthe patch.

In accordance with the principles of the present invention, in theexample of FIG. 4 the read pointer 62 may be set with all zeroes asshown on the right side of the read pointer. With this setting the delayline is disabled, since no signal samples from the element e_(n) areapplied to the output bus bn. Other techniques may alternatively beemployed to prevent signals from an array element from being put on thebus. In the example of FIG. 5 a single switch 72 such as a passgate isused at the output of the delay line. This configuration is suitable foruse for either a parallel or serial configured delay line. Anothertechnique shown in FIG. 6 is to use a tristate buffer 74. The tristatebuffer 74 is controlled by a control line 76 to either transmit theinput signal from the delay line to the tristate buffer output, or setthe tristate buffer to exhibit a high output impedance. In one settingof the control line 76 the tristate buffer will produce a high or lowvoltage or current signal as determined by the echo signal, or a high(e.g., open circuit) impedance output. Passgates and tristate buffersmay be readily implemented in microcircuitry suitable for use in amicrobeamformer.

FIG. 7 illustrates a design for a two dimensional array andmicrobeamformer combination of the present invention which has twopatches bussed to the same main beamformer channel. In this example themicrobeamformer delay channels of two patches, P₁ and P_(n), are coupledto a common bus bn, which is coupled by a cable conductor 16 n to achannel of the mainframe beamformer. FIG. 7 is a top plan view of thetwo dimensional array, with the microbeamformer attached to the bottomof the array and not visible in this drawing. Each patch in this examplecomprises sixteen elements arranged in a 4 row (r₁-r₄) by 4 column(c₁-c₄) patch. Thus, thirty-two transducer elements are connected to thesame main beamformer channel in this example. Since patches P₁ and P_(n)share the same beamformer channel, the elements of only one of these twopatches can use bus bn at any given time. This means that a “buffer” ofelements of the length of three columns of elements must separate themaximum aperture length from the second interconnected patch P_(n), asshown by the bracket marked “buffer.” The maximum receive aperture sizewill thus have a maximum length of A_(L) and a maximum height of A_(H)as shown in the drawing. For instance, an initial receive aperture caninclude the elements of patch P₁ and all of the elements of the patchesup to the left side of the buffer region. As this aperture is stepped tothe right, columns c₁ to c₄ of patch P₁ are successively disabled witheach step as the corresponding four columns of the elements in thebuffer region are successively enabled. At the end of the third step ofthis four-beam step, only the elements of column c₄ of patch P₁ will beenabled and all three columns of elements of the buffer region will beenabled and contributing to the active aperture. With the next rightwardstep of the aperture, the last column c₄ of patch P₁ will be turned offand the first column c₁ of patch P_(n) will be turned on. The activeaperture at this moment will thus consist of all of the elements to theright of patch P₁ and through and including the first column of patchP_(n). Thus, there is never a time when elements from both commonlybussed patches are using the bus at the same time. The design rule forthis example is that the size of the buffer region is at least equal tothe number of columns of a patch minus one.

In this example patches in the height dimension do not share the samebus. Thus, there is no restraint on the maximum size of the activeaperture in the height dimension. The maximum aperture size in theheight dimension, A_(H), may thus be equal to the full height dimensionof the two dimensional array.

FIG. 8 illustrates a design for a two dimensional array in which fourpatches share the same main beamformer channel. As in FIG. 7, the twodimensional array 12 of FIG. 8 is shown in a top plan view with themicrobeamformer located beneath the array. Four patches P₁, P₂, P₃, andP₄ are all coupled to bus bn by buses bn₁, bn₂, bn₃, and bn₄,respectively. Simultaneously present signals are summed on the bus andcoupled to a channel of the main beamformer by conductor 16 n of thecable 16. The maximum receive aperture of the array exhibits dimensionsof A_(L) and A_(H). The maximum aperture is shown when positioned at thecorners of the array as apertures Ap1, Ap2, Ap3, and Ap4. The maximumaperture positions are separated by a buffer region of buf_(L) in thelength dimension and a buffer region of buf_(H) in the height dimension.The horizontal length of the buf_(L) region is one element less than thehorizontal length of a patch and the vertical height of the buf_(H)region is one element less than the vertical height of a patch. In acase where the patches and the elements are square these regions will beof the same size. In a case where the patch dimensions and/or theelement dimensions are not square these region sizes will differ. In theexample of FIG. 8 it is seen that, as the receive aperture starts fromposition Ap1 and is stepped to the right, columns of the P₁ patch (andall patches above it in the aperture) are successively disabled ascolumns of elements in the buf_(L) region are successively enabled. Asthe aperture is stepped fully to the right of patch P₁ and the entirepatch is disabled, the leftmost column of the commonly bussed patch P₂is enabled. The active aperture continues to be stepped to the right inthis manner, with the final aperture location as shown by Ap2. Thus,there is never a time when elements from patches P₁ and P₂ are enabledat the same time. Commonly bussed patches P₃ and P₄ are disabled at thistime since the uppermost extent of the active aperture is below thesepatches. While the maximum height of the active aperture is shown asA_(H) in this example, it will be realized that this dimension can beincreased by the height of the buf_(H) region in the case where theaperture is being stepped to the right.

Thereafter, or alternatively, the aperture may be stepped upward fromthe Ap1 position. As the aperture is stepped up a patch row at a time,the rows of elements of patch P₁ are successively disabled from thebottom to the top, and rows of elements in the buf_(H) region above theaperture area Ap1 are successively enabled in correspondence. After(m−1) such steps only the upper row of patch P₁ (and all patches to theright of patch P₁ in the aperture) will be enabled and all (m−1) rows ofelements in the buf_(H) region above the aperture area Ap1 will beenabled. With the next aperture step (bringing the step total to m), allm rows of patch P₁ will be disabled and the first row of patch P₃ willbe enabled, along with all of the rows of the buf_(H) region in theaperture. Thus, there is never a time when elements from both patches P₁and P₃ are contributing to the beam. Upward stepping of the aperturecontinues in this manner until the aperture reaches its upper limit oflocation Ap3. As in the case of horizontal translation, it will berealized that the length of the aperture in this situation could beequal to A_(L) plus the length of buf_(L).

Allowing for a buffer region in both the horizontal and vertical (heightand length) dimensions allows translation of the maximum aperture in anydirection, including diagonal translation. For example, the aperture maybe stepped diagonally from position Ap1 by simultaneously moving theaperture to the right and up one element in each step. The aperture cancontinue to be moved diagonally in this manner to a final apertureposition Ap4. As indicated by the dashed aperture outline ApD, with amaximum aperture size of A_(L) by A_(H) and buffer regions as shown,only elements from a single patch will contribute to the signals on busbn at any point in time during this aperture translation. The dashedoutline ApD shows the aperture just after leaving the location whereonly the upper right corner element of patch P₁, of the four commonlybussed patches, contributed to the signals on bus bn, and now located ata location where only the lower left corner element of patch P₄contributes to the signals on bus bn. The example of FIG. 8 enableshorizontal, vertical, and diagonal stepping of a maximum receiveaperture in a two dimensional microbeamformed array in which the numberof patches is (with the exception of the buffer dimensions) four timesthe number of cable conductors and main beamformer channels. The 4:1pattern of patches to main beamformer channels can be extendedsymmetrically throughout the two dimensional array of FIG. 8. With evenlarger ratios of array size to maximum aperture size, greater numbers ofpatches can be interconnected, as shown by the common connection ofthree patches in the horizontal dimension in the example of FIG. 3.

The switching elements shown in FIGS. 4, 5, and 6 are functionallyequivalent to single pole, single throw switches. The following examplesof the present invention use the functional equivalent of single pole,double throw switches to shift the receive aperture. These examplesprovide the benefit that the patch boundaries are effectivelyrepositioned as the aperture is shifted. A further benefit of thefollowing examples is that an identical number of element signals can bemaintained for each main beamformer channel, obviating the need toperform apodization weighting adjustment for channels with differentnumbers of signals. FIG. 9 shows one such example, using the same twodimensional array configuration as FIG. 3. The delay lines DL for eachelement in row R1 are shown attached to the respective elements of rowR1. A single pole, double throw switching element Sw is connected at theoutput of each delay line DL. The outputs of these switching elementsconnect the delay lines to one of two possible busses, cable conductors,and main beamformer channels, depending upon the setting of the switcharm. In this example each patch consists of five elements, and when theswitches Sw are set as shown in FIG. 9 it is seen that the delay linesfor elements e6-e10 are all coupled to bus b2 which sums the signalsfrom those five elements. The patch of these five elements is indicatedby dashed lines 102, 104 extending across the two dimensional array 12.The summed signal on bus b2 is coupled by cable conductor 16 b to achannel of the main beamformer for the completion of beam formation.Similarly, the patch consisting of elements e11-e15 between dashed lines104, 106 has its received signals coupled to and summed on bus b3, thencoupled by cable conductor b3 to a main beamformer channel. In likemanner five-element patch signals are summed on busses b4 (e16-e20) andb5 (e21-e25) and coupled over conductors 16 d and 16 e to mainbeamformer channels. The arrows below the busses indicate connections tothe delay lines from other patches which share the same busses and mainbeamformer channels at other times in the aperture shifting. It is seenin this example that each bus is summing the signals from a fullcomplement of five elements, the size of a patch used in this example.

The switching elements Sw are functionally equivalent to single pole,double throw switches. That is, the output of a delay line is coupled toone of two output busses and main beamformer channels, depending uponthe setting of the switch. This arrangement makes the boundaries of apatch entirely arbitrary, depending upon the setting of a switch. FIG.10 illustrates a basic form of a single pole, double throw switch 120,with the arm 122 determining whether the signal from a delay line DL iscoupled to bus x or bus y. FIG. 11 illustrates another example, in whichthe function of a single pole, double throw switch is provided by twoparallel single pole, single pole switches 124 and 126. In the exampleof FIG. 9 a full complement of elements equal to the number of elementsforming a full patch, five in this example, are coupled to each mainbeamformer channel. The setting of the switch Sw for a particularelement determines the main beamformer channel to which the element iscoupled and hence the patch group of which the element is a contributorat a given point in time.

FIG. 12 illustrates the configuration of FIG. 9 after the aperture hasbeen shifted one element to the left, as indicated by the dashed lines102′, 104′, etc. in relation to the original patch boundary lines 102,104, etc. The switch Sw for delay line 5 has been reset to its alternatesetting, coupling the signal from delay line 5 to conductor 16 b. Theswitch Sw from delay line 10 has also been reset, redirecting the signalfrom delay line 10 from conductor 16 b to conductor 16 c. Similarly, theswitches Sw for each fifth delay line, including illustrated delay lines15 and 20, have been reset to their alternate settings. These switchsettings combine the signals from elements e5-e9 on conductor 16 b, thesignals from elements e10-e14 on conductor 16 c, the signals fromelements e15-e19 on conductor 16 d, and so forth. Compared to thesignals on the conductors in FIG. 9, it is seen that the elementgroupings on each conductor have been shifted to the left by one elementand hence the entire aperture has been shifted to the left by one arrayelement.

In FIG. 13 the aperture is shifted one element to the right in relationto its starting position in FIG. 9, as indicated by patch boundaries100″, 102″, 104″, 106″, etc. Only illustrated switches Sw for delaylines 6, 11, 16, and 21 are in their original settings; all of the otherswitches have been reset. This resetting causes the signals from delaylines 7, 8, and 9 to be coupled to the extension b3′ of bus b3 insteadof their previous coupling to bus b2. As a result, the signals fromelements e7-e11 are now combined on bus b3 and coupled to a mainbeamformer channel by way of conductor 16 c. Similarly, the signals fromelements e2-e6 are coupled to conductor 16 b, the signals from elementse12-e16 are coupled to conductor 16 d, and so forth. It may be seen thateach patch grouping on a conductor has been shifted to the right by oneelement compared to the original settings, and hence the entire aperturehas been shifted to the right by one element.

FIG. 14 illustrates the switch Sw settings when the aperture is shiftedanother element to the right in relation to FIG. 13. The switch Swpositions of FIG. 14 differ from those of FIG. 13 in that the switchesfor delay lines 7, 12, 17, and 22 have been reset to their alternatesettings. This causes the signals from elements e3-e7 to be directed toconductor 16 b, the signals from elements e8-e12 to be directed toconductor 16 c, the signals from elements e13-e17 to be directed toconductor 16 d, and so forth. The entire aperture has been shifted tothe right by another element as indicated by dashed lines 100′″, 102′″,104′″, and so on.

By setting the switches Sw from delay lines 8, 13, 18, and 23 in thenext iteration, it will be seen that the aperture is shifted to theright by a further element. The aperture can be shifted across the arrayin this manner. In every case it is seen that, with the exception of thephysical edges of the array, an equal complement of element signals isalways present at each main beamformer channel at each apertureposition. This technique can be used with a one dimensional array forwhich the aperture is to be shifted in only one direction, the azimuthdirection. The technique can be employed to additionally shift theaperture in the orthogonal (elevation) direction on a two dimensionalarray by, for instance, adding an orthogonally configured single pole,double throw switch parallel to the first one, or using a single pole,3-throw switch or its equivalent for each element. To accommodatediagonal translation in addition to azimuth and elevation translations,a single pole, 4-throw switch or its equivalent can be used to connectan element to any one of four possible cables and main beamformerchannels. Each output of the single pole, n-throw switch is connected toa different cable conductor and hence a different main beamformerchannel.

In many linear array implementations the beams are always (or most ofthe time) steered straight ahead, normal to the surface of the array.When there is no off-axis steering in such a straight-ahead beamsteering implementation the aperture delays can be symmetrical about thecenter of the aperture. This means that patches at an equal distance oneither side of the aperture center use the same main beamformer delayand hence can be coupled to the same main beamformer channel. Oneskilled in the art will realize that such an implementation does notneed to use the buffer regions discussed above due to such symmetry. Thecoupling of separated patches to the same main beamformer channel shouldbe done in consideration also of the phased array requirements for thesystem, as the steering of beams in three dimensions requires continuousdelay differentiation across the phased array aperture.

Various applications and modifications of the above principles of thepresent invention will readily occur to those skilled in the art. Aspreviously mentioned, the 2D array transducer can be planar (flat), orbent or curved in one or several dimensions. Digitizing of the echosignals can be performed in the probe or in the system mainframe.Amplification can be employed in either the probe, the system mainframe,or both. The microbeamformer circuitry shown above for echo receptioncan also be used in part for transmit beamforming. Additionalmodification are within the scope of the present invention.

1. An ultrasonic diagnostic imaging system for imaging a volumetricregion with a sequence of translated receive apertures comprising: anarray of transducer elements, local groups of which comprise patches ofelements having a width dimension; a multi-channel beamformer producinga beamformed output signal; and a microbeamformer including a pluralityof delay lines, each delay line having an input coupled to an arrayelement and an output producing a delayed signal which may be directedto channel of the multi-channel beamformer; and a source of controlsignals, coupled to the microbeamformer, which act to control thedirection of delay line outputs to channels of the multi-channelbeamformer, wherein a receive aperture formed by the elements ofmultiple patches may be stepped from one aperture location of thetransducer array for one beam to another aperture location of thetransducer array for another beam in a step increment which is less thanthe width of a patch of elements.
 2. The ultrasonic diagnostic imagingsystem of claim 1, wherein the outputs of delay lines coupled toelements of different patches are coupled to a common channel of themulti-channel beamformer.
 3. The ultrasonic diagnostic imaging system ofclaim 1, wherein the outputs of the delay lines are coupled to channelsof the multi-channel beamformer by the functional equivalent ofswitches.
 4. The ultrasonic diagnostic imaging system of claim 3,wherein the delay lines are responsive to enabling signals and whereinthe source of control signals provides enable signals to the delaylines.
 5. The ultrasonic diagnostic imaging system of claim 4, whereinan enable signal acts to enables the coupling of a delayed signal of adelay line to a channel of the multi-channel beamformer, wherein anenable signal provides the functional equivalent of a closed switch. 6.The ultrasonic diagnostic imaging system of claim 5, wherein the lack ofan enable signal provides the functional equivalent of an open switch.7. The ultrasonic diagnostic imaging system of claim 1, wherein thedelayed signals from the elements of a given patch may be directed to acommon beamformer channel.
 8. The ultrasonic diagnostic imaging systemof claim 7, wherein the control signals from the source of controlsignals determine which delayed signals from the elements of a givenpatch are directed to the common beamformer channel.
 9. The ultrasonicdiagnostic imaging system of claim 1, wherein a receive aperture formedby the elements of multiple patches may be stepped from one aperturelocation of the array transducer for one beam to another aperturelocation of the array transducer for another beam in a step increment ofone element.
 10. A method of translating a receive aperture of an arrayof ultrasonic transducer elements, the aperture being a group ofelements, the elements of the aperture being arranged in local groups ofpatches with a patch having a width dimension, comprising: receivingsignals from the elements of an aperture which is located in a firstlocation on the array; translating the aperture from the first locationto a partially overlapping second location which is translated in aselected direction from the first location by: receiving signals fromelements common to the two aperture locations, receiving signals fromadded elements adjacent to and beyond a side of the aperture in thefirst location which is in the selected direction, and not receivingsignals from a complementary number of elements at the opposite side ofthe aperture in the first location, wherein the number of added elementsin the selected direction is less than the width dimension of a patch.11. The method of claim 10, wherein the elements of each patch of anaperture are separately delayed and the delayed signals summed togetherat a summing node.
 12. The method of claim 11, wherein the elements of aplurality of patches not included in the aperture share the summingnodes of patches included in the aperture, wherein the patches sharing asumming node are not active at the same time.
 13. The method of claim10, wherein receiving signals from added elements includes adding someof the elements of a first patch on one side of the aperture to theaperture and not receiving signals includes not receiving signals froman equal number of elements of a second patch on the opposite side ofthe aperture.
 14. The method of claim 13, further comprising a pluralityof delay lines coupled to respective ones of the elements of the array,with the outputs of the delay lines of the elements of a patch beingcoupled to a common summing node, wherein the first patch and the secondpatch are coupled to the same summing node.
 15. The method of claim 14,wherein receiving signals further comprises enabling the passage ofsignals from the delay lines of the elements included in an aperture.16. The method of claim 15, wherein receiving signals further comprisesswitching signals delayed by the delay lines so that the delayed signalsare applied to summing nodes.
 17. The method of claim 16, furthercomprising a multi-channel beamformer having a plurality of beamformerchannels, each responsive to the signals received by a respectivesumming node.
 18. The method of claim 10, further comprising amulti-channel beamformer having a plurality of beamformer channels, eachresponsive to the signals received by a respective patch of elements.19. The method of claim 15, wherein enabling the passage of signalscomprises closing the functional equivalent of a single pole, singlethrow switch.
 20. The method of claim 10, wherein the second location isin one of two orthogonal directions relative to the first location.